There have also been cases where a customer violated Amazon's terms of service and lost access to all of their Kindle e-books. Amazon has all the power in this relationship. They can and do change the rules on us lowly peasants from time to time.
Note, there are indeed ways to download your books and import them into something like Calibre (and remove the DRM from the books). If you do some web searches (and/or search YouTube) you can probably figure it out.
I hate that pirating is the ONLY way to even semi own what you buy. Bought an album off Bandcamp (DRM free music) and when one of the songs on that album got in a pointless argument about copyright and got taken down from my Spotify playlists.
Songs being taken off of Spotify is really common if you're into older stuff as the rights get passed on when the artist dies. Though in this case it was a year old album.
I was glad I bought it DRM free as I thought they could only unlist it from the store, not from libraries... until I saw it was gone there too.
I payed MONEY for them to take it out of my library on a DRM free site. That's like them taking my music CD and scratching it with sandpaper.
Pirating literally gives me the same experience as buying it for literally no issue. (except the lossless files but who cares)
For ebooks in particular, owning what you buy isn’t that difficult though. You can legally buy DRM protected epubs in a lot of online book stores and then use the software calibre (open source) to strip the DRM. Much easier than with music, movies or software.
Some songs get taken down and relisted under different albums. I've had this happen with a lot of lofi music I thought was gone. Worth double checking!
I‘d recommend the software calibre. Great for managing your ebook library and it can convert epub into amazons azw, mobi or kfx formats (depending on which generation kindle you have). With the right plugin you can even create WordWise data for your kindle-converted ebooks.
You don’t even necessarily need to illegally download the books, as calibre can also handle the DRM of .ebub books you bought from almost any store. Of course, sailing the seven seas is still always an option though.